Severe Thunderstorm Warning 168, NWS St. Louis, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
150 PM CDT SAT JUL 6 2002

RETROGRESSION OF THE UA PATTERN ACRS NOAM UNDERWAY MUCH AS THE MDLS
HV BEEN ADVERTISING.  UPR HI WHICH WAS OVR THE WRN OH VLY YDA MRNG
HAS SHIFT WWD INTO THE MS VLY.  MDLS SHOW THE PATTERN SHIFT CONTG
INTO THE FCST PD AS THE UPR RDG BCMS WELL ESTABLISHED IN THE WRN
U.S. WITH TROFG OVR THE ERN U.S. AND NWLY FLOW SETTING UPR OVR THE
MIDWEST.  WRT TO THIS TRANSITION...WHILE ALL THE MDLS ARE SHWG THIS
PATTERN CHG...THE ONE DIF TDA WHICH CONTS FM THE LAST FEW DAYS IS
THE AMT OF AMPLIFICATION OF THE ERN TROF.  THE MDLS CONT TO DIFFER
AMG THEMSELVES AND WITH EACH RUN.  THE CAN AND ECMWF WERE THE CDST
00Z RUNS AND NOW THE 12Z AVN IS COMING IN LN WITH THEM AT LEAST
WED-THURS.

THE INITIAL IMPACT OF THIS GRDL PATTERN CHG HAS BEEN THE SHIFT OF
THE SFC MOIST AXIS WWD AS DRIER AIR ADVCTS IN FM THE OH VLY WITH
HI PRES BLDG SWD FM THE GRTLKS IN RESPONSE TO THE UPR LOW/TROF
OVR THE NE U.S..  THERE IS NO DEFINED BACKDOOR FNT RATHER A DIFFUSE
ZN...THE MOST IMPORTANT OF WHICH IS THE ERN EDGE OF HIER SFC DPTS
WHICH RUNS FM ERN IA TO NR THE MS RVR.  AS HAS BEEN THE CASE THE
LAST FEW DAYS ISOLD PULSE CNVCTN IS TRYING TO DVLP IN THE CU FIELD
BUT IS STRUGGLING.  SEEMS THE BEST CHC FOR ANY CNVCTN THIS AFT AND
EVNG WUD BE NE MO WHERE WELL-DEFINED OUTFLOW BNDRY FM THE IL MCS MAY
INTERACT WITH THE ERN EDGE OF THE DPR MSTR/MOST UNSBL AMS.  OTW THE
MDLS ALL AGREE THAT THE DRIER AIR OVR THE OH VLY WL CONT TO ADVCT
WWD ACRS THE CWFA TNGT BRINGING LESS HUMID CONDS FOR SVRL DAYS.
THIS WL BE SPCLY TRUE IN THE IL ZNS WHERE DPTS HV ALREADY FALLEN
INTO THE U50S.  WITH THIS WWD SHIFT IN THE UPR HI AND LOW LVL MSTR
AXIS IT SEEMS THE THREAT OF DIURNAL CNVCTN SHUD WANE.  IT APPEARS
OVR THE NEXT 36H THE BEST THREAT WUD AGAIN BE NE MO WHERE BNDRY FM
CURRENT ACTVTY MAY IMPACT...AND WHERE THE ETA ALSO SUGGEST THERE MAY
BE A RESIDUAL BNDRY ON SUN.  OTW WILL HOLD OFF ANY MENTION OF PCPN
UNTIL THE NEXT LRG SCALE FNT WHICH CONTS TO BE ADVERTISED FOR TUE
AFT-WED MRNG TIME FRAME.  WL LET THE HEAT WRNG FOR THE CITY OF ST
LOUIS EXPIRE AT 400 PM AS THE HIS HV BEEN WELL BLO CRITERIA. TMPS
SHUD MOD DOWNWARD A TAD OVR THE NEXT DAY OR TWO...SPCLY MINS WITH
THE LOWER SFC DPTS.

.STL...NONE
GLASS